Migrant labourers in India face increased heat stress driven by climate warming and ENSO variability

Abstract

Migrant labourers typically work long hours at physically demanding tasks without air conditioning, and they account for a considerable fraction of India’s population — a share that is increasing with urban growth. However, changes in heat stress and labour capacity in major urban centres that attract rural-to-urban work migrants remain unexplored. Moreover, it remains unclear how the increased heat stress and reduced labour capacity under the warming climate will alter the most preferred workplaces for migrant labourers in India. Here, we use station-based observations, reanalysis, and climate model projections to reconstruct trends and variability in heat stress metrics, including wet-bulb temperature (Tw for indoor exposure) and wet-bulb globe temperature (WBGT for outdoor exposure). We show that during 1980-2021, most rural-to-urban migration hotspots in north, east, and southern India witnessed a significant (p < 0.05) rise in Tw, indicating elevated indoor heat stress. Over that interval, outdoor heat stress has considerably increased and led to a ~10% decline in labour capacity in these hotspots. A substantial rise in the indoor and outdoor heat stress exposure of migrants and a reduction in their physical labour capacity is projected with each additional degree of global warming. El Nino-Southern Oscillation variability can also significantly enhance these effects. Effective mitigation and adaptation options are needed to reduce the risks migrant workers face due to increasing indoor and outdoor heat stress in India.